The present invention relates to a polyethylene naphthalate multilayered film for a high density magnetic recording medium. More specifically, the present invention relates to a polyethylene naphthalate multilayered film as a base film for a high density magnetic recording medium, having a high strength both in machine and transverse directions, being excellent in abrasion resistance and having preferred surface properties.
In recent years, a polyethylene naphthalate film having a high strength both in machine and transverse directions of the film has been considered to be promising as a base film for high density magnetic recording media, in particular, for future HDTV digital video equipments and the development thereof has now been conducted.
However, the polyethylene naphthalate film having a high strength has a drawback that particles contained in the film tend to drop out readily. In order to overcome this problem, although particles having a hard dropping-out property has been developed positively, such particles having a hard dropping-out property tend to coagulate and as a result, a defect of worsening the surface properties of the film takes place.
The high density magnetic recording medium described herein means video tapes for 8 mm track video or C-cassette, and also video tapes for HDTV such as a high vision TV, which are expected as new media in the next generation. This is particularly used suitably to the application use of vapor deposition-type video tapes including vertical magnetization-type.
For overcoming the foregoing drawbacks, as a result of the present inventor's earnest study, it has been found that by laminating a polyethylene naphthalate layer (B) having the specific surface characteristics and a thickness of not more than 2 .mu.m on at least one surface of a polyethylene naphthalate layer (A) by coextrusion method, the obtained polyethylene naphthalate multilayered film has the Young's modulus of not less than 700 Kg/mm.sup.2 in both of the longitudinal and transverse directions of the film, can prevent dropping-out of particles without worsening the surface properties of the film and is extremely useful as a film for high density magnetic recording medium. The present invention has been attained based on the finding.